The present invention relates to rotary fluid pressure devices, and more particularly, to such devices of the type including a fluid displacement mechanism which comprises a gerotor gear set.
Although the present invention may be included in a gerotor-type device being utilized as a pump, it is especially adapted for use in a low-speed, high-torque gerotor motor, and will be described in connection therewith.
For years, many of the gerotor motors made and sold commercially, both by the assignee of the present invention as well as by others, have had the motor valving disposed "forwardly" of the gerotor gear set (i.e., toward the output shaft end of the motor), thus having nothing disposed "rearwardly" of the gerotor gear set except for an endcap. The present invention is not so limited, but is especially adapted for use with gerotor motors of this type, and will be illustrated and described in connection therewith.
In many vehicle applications for low-speed, high-torque gerotor motors, it is desirable for the motor to have some sort of parking brake or parking lock, the term "lock" being preferred in some instances because it is intended that the parking lock be engaged only after the vehicle is stopped. In other words, such parking lock devices are not intended to be dynamic brakes, which would be engaged while the vehicle is moving, to bring the vehicle to a stop. However, the term "brake" will generally be used hereinafter to mean and include both brakes and locks, the term "brake" being somewhat preferred to distinguish from a device which would operate either fully engaged or fully disengaged.
For many years, those skilled in the art have attempted to incorporate brake and lock devices into gerotor motors, as opposed to merely adding a brake package on the motor output shaft. Examples of such devices are illustrated and described in U.S. Pat. Nos. 3,616,882 and 4,981,423. In the device of U.S. Pat. No. 3,616,882, a braking element is disposed adjacent the forward end of the gerotor star, and is biased by fluid pressure into frictional engagement therewith. Such an arrangement involves a certain degree of unpredictability of performance, in view of variations in clearances, etc. Such an arrangement also requires a substantial redesign of the wear plate and forward bearing housing of the motor. In the device of U.S. Pat. No. 4,981,423, there is a multi-disc brake assembly which is of the "spring-applied, pressure-released" type. The arrangement of U.S. Pat. No. 4,981,423 also requires almost total redesign of the forward bearing housing, and also results in a much larger bearing housing. In addition, the disc pack is in splined engagement with the output shaft and, therefore, must be able to brake or hold the full output torque of the motor, thus necessitating that the discs, the spring, and the apply/release piston all be relatively larger.
In many known motor brake and lock arrangements, the majority of the braking "torque" is provided by a set of brake discs. Typically, the brake discs are provided with some sort of friction material which, while effective in increasing the braking torque, also adds substantially to the cost of the brake discs. As a result, there are many vehicle applications where it would be desirable to utilize a low-speed, high-torque gerotor motor having a built-in brake, but wherein it is not economically feasible to do so because of the expense represented by typical brake discs provided with the necessary friction material.